# s = "Hello, Python world!"
# print(len(s))
# a=0
# for i in s:
#     if i =="o":
#        a+=1
# print(a)
# s=s.upper()
# s=s.lower()

# print(s.find("python"))
# s=s.replace("world","universe")
# if s.startswith("hello"):
#     print("是以hello开头的")
# else:
#     print("不是hello开头")
# if s.endswith("!"):
#     print("是以！结尾的")
# s=s.strip("!")
# s=s[::-1]
# s=s[7:13]
# s=s.lstrip("Hello")
# s1="Hello,"
# s2="World"
# s3=s1+s2
# print(s3)
# s=f"{s}{2021}"
# print(s.find("e"))
# print(s.count(" "))
# s=s.split(",")
# list=[]
# for i in s:
#     list.append(i)
# print(list)
# s=list
# s.sort()
# a=s.isnumeric()
# print(a)
# list = ['Hello,', 'Python', 'World!']
# rs=" ".join((list[0],list[1],list[2]))
# print(rs)
# s=s.lower()
# rw="number :%d"%100
# print(rw)
# a=s.islower()
# print(a)
# list=[1,2,3]
#
# rs="-".join(map(str,list))
# print(rs)
#
# b=0
# for i in s:
#     if i =="o" :
#         print(b)
#         b+=1
#     else:
#         b+=1
# s=s.replace("o","O",1)

# print(s)








# s = "Python is great!"
# a=""
# for i in s:
#    a=i+a
# print(a)
# s=s.replace(" ","_")
# print(s)
# s2 = "A man, a plan, a canal, Panama!"
# s3=''.join(filter(str.isalnum, s2)).lower()
# if s3==s3[::-1]:
#     print("true")
# else:
#     print("false")
# a=s.find("is")
# print(a)

# a=s.find("t")
# list=[i for i in s]
# list.insert(a+1,"_inserted")
# s="".join(map(str,list))
# print(s)

# s=s.replace("great","awesome",1)
# print(s)
# list=[i.upper() for i in s]